Conductive transparent films are employed for coating transparent electrodes of liquid crystal displays, electroluminescence displays, plasma displays, electrochromic displays, solar cells, touch panels and the like, and for coating substrates such as those made of electromagnetic shielding material. The most widely employed conductive transparent film is a vapor deposited film made of indium-doped tin oxide (i.e., ITO). However, the formation of ITO film by a vapor deposition process has problems such as the necessity of a high temperature for film formation and high cost for film formation. ITO film can be formed by a coating method. However, the film formation by this method requires a high temperature, the conductivity of the film depends on the degree of dispersion of ITO, and the haze value of the film is not always low. Furthermore, for an inorganic oxide film such as an ITO film, cracks tend to be generated by the bending of the substrate, so that the conductivity may be reduced.
On the other hand, a conductive transparent film made of conductive polymer that can be prepared at a low temperature and a low cost has been proposed as a conductive transparent film made of an organic material. As for the conductive polymer that can be used for such a film, Japanese Patent Publication No. JP 2636968 discloses a complex of poly(3,4-dialkoxythiophene) and a polyanion and a method for producing the complex. This complex has good water dispersibility. A thin film produced by applying a coating, composition containing an aqueous dispersion of the complex to a substrate has a sufficient antistatic function, but insufficient transparency and conductivity.
Japanese Laid-Open Patent Publication No. JP 8-48858 describes that a thin film produced by applying a coating composition to a substrate has an improved conductivity, wherein the coating composition is obtained by adding a compound that is selected from the group consisting of a compound having two or more hydroxyl groups, a compound having an amide group, and a compound having a lactam group to an aqueous dispersion containing a complex of poly(3,4-dialkoxythiophene) and a polyanion described in Japanese Patent Publication No. JP 2636968. Japanese Laid-Open Patent Publication No. JP 2000-153229 describes that a thin film produced by applying a coating composition containing a non-proton compound having a dielectric constant of ∈≧15 to a substrate and drying the resultant substrate at a temperature less than 100° C. has an improved conductivity.
The properties of all the coatings compositions described in these publications are improved by adding a specific compound to the water dispersion containing a complex of poly(3,4-dialkoxythiophene) and a polyanion described in Japanese Patent Publication No. JP 2636968, and the conductivities thereof are comparatively improved. However, the water dispersion containing the complex (i.e., a conductive polymer) is the same, so that the transparency and the conductivity of the resultant film obtained from the water dispersion are not necessarily sufficient.